Scientists have found stem cells in human ovaries from which it may one day be possible to produce an ‘unlimited’ supply of eggs.
The breakthrough discovery could revolutionise fertility treatment, according to experts.
Doctors in the U.S. were able to isolate the cells in a laboratory where they ‘spontaneously generated’ eggs which they say are capable of being fertilised.
Experts say the discovery challenges the prevailing view that women only have a certain number of eggs and can never produce any more, unlike men who go on producing sperm.
In this sense it ‘re-writes the rule book’ and could help infertile couples and also potentially allow women to remain fertile for longer, they added.
Researchers at Massachusetts General Hospital managed to locate egg-producing stem cells in the ovaries of reproductive age women and grow immature eggs, known as oocytes.
These appeared normal and when implanted in living human ovarian tissue – which was grafted inside mice – grew normally for two weeks.
Dr Jonathan Tilly, who led the study, said it ‘opens the door for development of unprecedented technologies to overcome infertility in women and perhaps even delay the timing of ovarian failure’.
He added: ‘These cells, when maintained outside of the body, are more than happy to make cells on their own and if we can guide that process I think it opens up the chance that sometime in the future we might get to the point of having an unlimited source of human eggs.’
His team found the stem cells by searching for a protein called DDX4, unique to the surface of egg cells.
For legal reasons, scientists cannot use these egg cells to create an embryo. But the same stem cells taken from mice were fertilised and produced embryos, according to the study published in the Nature Medicine journal. Dr Allan Pacey, a fertility expert at Sheffield University, told the BBC: ‘This is a nice study which shows quite convincingly that women’s ovaries contain stem cells that can divide and make eggs.
‘Not only does this re-write the rule book, it opens up a number of exciting possibilities for preserving the fertility of women undergoing treatment for cancer, or just maybe for women who are suffering infertility by extracting these cells and making her new eggs in the lab.’
One in six couples in Britain is estimated to have fertility problems, and the finite ‘biological clock’ of women has become more of an issue in recent years as rising numbers have delayed trying for motherhood.
Many have IVF treatment but there are often too few eggs donated or able to be harvested from a woman.
Rising numbers are also resorting to freezing their eggs – while they still have them – so they can perhaps pursue a career before trying to fulfil their dreams of motherhood.
Last year frozen embryos were used in 10,556 courses of IVF – nearly a fifth of the total – although fewer than a quarter of these are likely to have resulted in pregnancy.
The latest advance could, if it works in further trials, change all that.
Although using the technique in humans is probably some years away, Dr Tilly’s team is looking at putting the cells in a bank so they can be tested further and possibly used to improve IVF treatment and for women undergoing cancer treatment.
A woman has the most oocytes as a foetus, about seven million, dropping to about one million by birth, and 300,000 by puberty. By menopause, she has none left.
Since the Fifties, scientists thought that ovarian stem cells capable of producing new eggs were only active during in the womb as a baby develops.
Dr Tilly said this belief ‘was not actually based on data proving it was impossible, it was simply an assumption made because there was no evidence indicating otherwise’.